1. Field of the Invention
This invention relates generally to a control circuit for a brushless DC motor, and more particularly is directed to an improvement in the control circuit for a brushless DC motor so as to particularly suit the latter for the direct drive of a reel mount in a video tape recording and/or reproducing apparatus or VTR.
2. Description of the Prior Art
In a VTR or similar apparatus of the type employing video cassettes, after a cassette is operatively positioned in the apparatus, a tape loading device is actuated to withdraw magnetic tape from the cassette and to wind or wrap the withdrawn tape around a guide drum carrying rotating heads by which video signals can be recorded on, or reproduced from the tape guided by the drum. When a recording or reproducing operation has been completed, removal of the cassette from the apparatus has to be preceded by a tape unloading operation during which the tape is unwrapped from the drum and returned to the cassette. During such tape loading or unloading operation, one of the reel mounts with which the tape-up and supply reels in the cassette are respectively rotatably coupled should be locked against rotation while the other reel mount is rotatable. Thus, during the tape loading operation, the tape to be withdrawn from the cassette for wrapping about the guide drum is unwound only from the tape reel coupled with the unlocked reel mount and, similarly, during the tape unloading operation, the tape unwrapped from the guide drum is returned to the cassette by being rewound only on the tape reel coupled with the unlocked reel mount. As a result of the foregoing, there is no moving or shifting of the tape from one to the other of the reels within the cassette by reason of a tape loading operation followed by an unloading operation.
In a VTR according to the prior art, during a tape loading or unloading operation, one of the reel mounts is locked against rotation by means of a brake belt or brake shoe which is spring urged against a drum surface on that reel mount and which is disengaged or released from the drum surface to free the reel mount for rotation during a recording or reproducing operation upon energizing of an electromagnet or solenoid having its armature suitably connected with the brake belt or shoe. However, such arrangement for selectively locking a reel mount against rotation is disadvantageous in that it employs a relatively large number of mechanical components, has a high power consumption for operation of the solenoid so that it is not suitable for use in a battery powered, portable VTR, and is noisy in operation when the solenoid attracts its armature.